Counterfeiting is a serious problem around the world which not only disrupts normal commercial or non-commercial activities but also poses safety as well as security issues to the general public. Many types of anti-counterfeiting measures are dedicated to help fight counterfeiting. For example, genuine goods carry authentication devices such as authentication tags or codes to help verify authenticity of goods or products. However, even such authentication tags or codes can become the subject of rampant counterfeiting and enhanced security measures to combat counterfeiting are desirable.
High precision authentication devices such as those comprising phase modulation coded security patterns are very useful in combating counterfeiting because phase modulation coded information subsisting in the security patterns are very sensitive and are difficult to counterfeit. The moiré pattern is a good example of authentication devices comprising phase modulation coded security patterns which has been widely used to enhance reliability of authentication devices. The term ‘authentication device’ in the present context generally means authentication device for use in combating counterfeiting.
While phase modulation coded security patterns such as moiré or moiré-like patterns are a very useful anti-counterfeiting tool, their highly precise or delicate properties make them difficult to use for many applications such as consumer or retail applications.
U.S. Pat. No. 7,561,308 discloses a method of decoding a digitally encoded image which is embedded in a moiré or moiré like pattern using a sampling approach. The method includes taking a series of elongate rectangular image content samples from the digitized encoded image at a frequency corresponding to the line frequency used to encode the encoded image, in which the samples are oriented at the encoding angle used to encode the encoded image. This method requires the prior knowledge of the encoding line frequency and orientation angle α, and the quality of the resulting decoded image is not entirely satisfactory due to, for example, presence of residual encoding lines in the decoded image.
It would be advantageous if enhanced means to perform verification of security devices such as those utilizing proportions of moiré patterns can be provided.